The U.S. Justice Department has given its approval to the merger of American Airlines and US Airways, the last major hurdle for a deal that will create the largest airline in the world.

The two companies communicated that customers with existing tickets are unlikely to see any noticeable changes, but longer term, the effects could be significant. Owners of frequent-flyer miles for both airlines will remain valid until both programs are consolidated on an equal value basis.

The two carriers are the last to link up in the latest wave of U.S. consolidation, which includes: